The present invention generally relates to a network apparatus for use in building an IP (Internet Protocol) network and, more particularly, to a switching router for performing high-speed transfer (cut-through) of an IP datagram by use of an ATM (Asynchronous Transfer Mode).
With wide popularization of applications such as the WWW (World Wide Web), the quantity of information transferred over the Internet has been steadily increasing, thereby involving a problem as a bottleneck to the communication performance of the Internet, especially of the router, a network apparatus for transferring IP datagrams between adjacent networks. Datagrams as used herein represent data and/or programs. This problem is caused by that the transfer processing requires confirmation of destination for each of the IP datagrams.
To solve this problem, switching routers such as a label switching routine have been proposed in which the ATM switch is combined with a controller for performing transfer and control of IP datagrams. Specific schemes include a CSR (Cell Switch Router) disclosed on February 1997 in IETF (Internet Engineering Force) RFC (Request For Comments) 2098.
However, it is not taken into consideration for the switching routines such as the above-mentioned label switching router obtained by combining the ATM switch with the controller to cope with a fault occurring on the controller connected to the ATM switch. This may cause a problem in the transfer of IP datagrams between adjacent nodes. Therefore, the inventor hereof examined the case in which the controller fails. The following describes a result of this examination with reference to FIG. 6.
FIG. 6 shows a data relay controller 100 for performing transfer and control of an IP datagram, detecting data satisfying a particular condition in the transfer IP datagram, and controlling an ATM switch based on the result of the detection, an ATM switch 110 for switching between ATM cells, and an adjacent node 120 connected through an ATM line.
The adjacent node 120 and the data relay controller 100 presets a standard VC (Virtual Channel) route for transferring the IP datagram, or a so-called default VC route 140, on a given VP (Virtual Path) route 130 through the ATM switch 110. Normally, the IP datagram is transferred along the default VC route relayed by the data relay controller 100.
Then, when the IP datagram satisfying a certain condition is detected, the data relay controller 100 sets a VC route for directly connecting the destination of the detected IP datagram to the adjacent node 120 of the destination through the ATM switch 110, this VC route being referred to as a cut-through VC route 150. Between the adjacent nodes, IP datagrams are transferred over the cut-through VC route not relay by the data relay controller 100. This allows communication between the adjacent nodes 120 without confirming the destination of each IP datagram and performing transfer processing, thereby significantly enhancing the transfer performance of IP datagrams.
It should be noted that the communication route in the ATM is set by use of the VC route and the VP route 130 that bundles a plurality of VC routes. It should also be noted that a different network communicable only through the data relay controller 100 is originally provided between the adjacent nodes 120; in order to transfer IP datagrams directly between the adjacent nodes 120 through the cut-through VC route 150, each adjacent node 120 is mounted with a mechanism for encapsulating the IP datagrams addressed to the adjacent nodes 120 of the original IP datagrams.
Therefore, if IP datagrams are transferred between the adjacent nodes 120 through the data relay controller 100 in the above-mentioned constitution composed of the data relay controller 100, the ATM switch 110, and the adjacent nodes 120, occurrence of a fault on the data relay controller 100 connected to the ATM switch may disable the data transfer between the adjacent nodes 120 even if the ATM switch has no trouble.